/Engine/Plugins/Online/OnlineSubsystemSteam/Source/Public/OnlineEncryptedAppTicketInterfaceSteam.h
The encryption key used is the one configured on the App Admin page for your app on Steam portal. There can only be one data encrypting request pending, and this call is subject to a 60 second rate limit.
True on success, false on failure.
bool RequestEncryptedAppTicket ( void * DataToEncrypt, int SizeOfDataToEncrypt )